Free-standing internally insulating liner

ABSTRACT

An insulating liner for use with exhaust system or pollution control devices such as catalytic converters and diesel particulate filters or traps. The insulating liner is shown in relation to an end cone for use with a catalytic converter. The end cone includes an outer metallic end cone and a free-standing insulating cone positioned within the outer metallic end cone. A substantial portion of the inner surface of the insulating liner is exposed to hot exhaust gas from an internal combustion engine. The insulating liner is preferably formed of a composite containing inorganic fibers and/or particles, which makes the insulating liner rigid, yet capable of withstanding repeated mechanical and thermal shocks.

[0001] This application is a divisional of U.S. Ser. No. 08/665,606,filed Jun. 18, 1996, now allowed, the disclosure of which is hereinincorporated by reference.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to exhaust system and pollutioncontrol devices, such as catalytic converters, diesel particulatefilters or traps, exhaust pipes and the like. In particular, theinvention relates to an internal insulating liner used in hightemperature applications. The application describes the invention as itrelates to an internally insulating end cone used to provide atransition from an exhaust pipe to the pollution control device. The endcone comprises a metal inlet or outlet cone housing with a free-standingfiber-based composite cone positioned within the metal cone housing. Theinternal fiber based cone does not require a protective metal internalcone housing.

[0003] Pollution control devices such as catalytic converters and dieselparticulate filters or traps are well known, and are most typically usedto purify the exhaust gasses produced by internal combustion engines.These types of pollution control devices typically comprise a metalhousing with a monolithic element securely mounted within the casing bya resilient and flexible mounting mat.

[0004] Two types of devices are currently in wide spread use—catalyticconverters and diesel particulate filters or traps. Catalytic converterscontain a catalyst, which is typically coated on a monolithic structuremounted in the converter. Monolithic structures are typically ceramic,although metal monoliths have been used. The catalyst oxidizes carbonmonoxide and hydrocarbons, and reduces the oxides of nitrogen inautomobile exhaust gases to control atmospheric pollution. Dieselparticulate filters or traps are wall-flow filters which havehoneycombed monolithic structures typically made from porous crystallineceramic materials. Alternate cells of the honeycombed structure aretypically plugged such that exhaust gas enters one cell and is forcedthrough the porous wall of one cell and exits the structure throughanother cell.

[0005] Due to the relatively high temperatures encountered in pollutioncontrol devices, it is important that the device be well insulated.Insulation is typically provided by securely mounting the monolithicelement within the casing using an insulating mounting mat comprised ofa suitable material. In addition, inlet and outlet cones which provide atransition from the exhaust pipe to the pollution control device arealso insulated. The inlet and outlet end cones have previously beeninsulated by providing a double-walled end cone comprising an outermetal housing and an inner metal housing, with a gap defined between theinner and outer cone housings. A suitable insulating material fills thegap between the inner and outer cone housings. Examples of dual-wall endcones can be seen, for example, in U.S. Pat. No. 5,408,828 to Kreucheret al. Kreucher et al. shows the catalytic converter having a two-walleddefuser leading from an exhaust pipe to the catalytic converter. Athermal insulating air barrier is provided between the inner wall andouter wall. Another example of double-walled end cones is seen in GermanPatent No. 3,700,070 A1 which shows an insulating mat placed between anouter and inner end cone.

[0006] The use of double-walled end cones has been required due to thenature of the insulating material used in pollution control devices. Inparticular, the use of low-density fibrous insulating materials requiresan inner cone, because exposure to exhaust gases causes rapid erosionand destruction of the low-density fibrous insulating material. Inaddition, as it erodes the fibrous insulating material tends to clog themonolithic structure of the pollution control device and degrade itsperformance. Thus, the protective inner end cone was required tomaintain the position and structural integrity of the insulatingmaterial. This is also true with other insulating materials which havebeen used as ceramic beads, such as shown in U.S. Pat. No. 5,419,127 toMoore, III. Moore shows an insulated exhaust manifold having a layer ofinsulating ceramic beads between an inner and outer exhaust manifold.

[0007] Although required for maintaining the position and structuralintegrity of the insulating layer of the inlet and outlet cones, the useof a protective metal inner cone has several disadvantages. Inparticular, use of an inner metal cone significantly increases theweight of the device, as well as the cost to manufacture the device.Therefore, what is needed is an insulating end cone which does notrequire use of a protective inner cone, and insulating material which isresistant to damage caused by exposure to hot exhaust gases and roadshock.

SUMMARY OF THE INVENTION

[0008] The present invention provides a self-supporting insulating linerfor use with exhaust systems and pollution control devices. Theapplication describes the invention as it relates to an insulating endcone for use with pollution control devices such as catalytic convertersand diesel particulate filters or traps. The end cone comprises an outermetallic end cone for connection to an exhaust system and a pollutioncontrol device. Within the outer end cone is a insulating conepositioned such that a substantial portion of the inner surface of theinsulating cone is exposed to hot exhaust gases from the internalcombustion engine, and the outer surface of the insulating cone ispositioned adjacent the outer metallic end cone. The self supportinginsulating liner thus eliminates the need for an inner metallic liner toprotect the insulation. In a preferred embodiment, the insulating lineris formed of a composite material which utilizes glass or ceramic fibersmixed with a binder to create a rigid, yet shock resistant insulatingend cone.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 shows a cross-sectional view of a prior art catalyticconverter having inner and outer metallic end cones.

[0010]FIG. 2 is a cross-sectional view of a catalytic converterutilizing the end cone of the present invention.

[0011]FIG. 3 is a cross-sectional view of an alternative embodiment ofthe end cone of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Referring now to the Figures, FIG. 1 shows a catalytic converter10 typical of the prior art. Catalytic converter 10 comprises metalhousing 12 with generally conical inlet 14 and outlet 16. The housing,which is also referred to as a can or a casing, can be made fromsuitable materials known in the art, and is typically made of metal.Preferably, the housing is made of stainless steel. Disposed withinhousing 12 is a monolithic catalytic element 18 formed of a honeycombedmonolithic body either of ceramic or metal. The surrounding monolith 18is a mounting and insulating mat 22.

[0013] Referring now to inlet 14 and outlet 16, it can be seen thatinlet 14 and outlet 16 comprise an outer end cone housing 26 and aninner end cone housing 28. An insulating material 30 is positionedbetween outer cone housing 28 and inner cone housing 26. As discussedabove, inner cone housing 28 is provided in prior art pollution controldevices to retain insulating material 30 in position and to preventinsulating material 30 from being damaged by hot exhaust gases passingthrough the pollution control device. However, the use of inner conehousing 28 adds additional weight, complexity and cost to the pollutioncontrol device. It is therefore desired to make the use of inner conehousing 28 unnecessary.

[0014] The present invention provides a free-standing internallyinsulating liner, and in particular an insulating end cone that does notrequire use of inner cone housing 28. In particular, the presentinvention utilizes a refractory material to provide an inner insulatingcone which is resistant to damage caused by exhaust gases as well asresistant to damage caused by mechanical and thermal shock. The usefulrefractory materials are capable of withstanding large gradients intemperature over short periods of time without shattering. Temperaturegradients can vary from sub-zero temperatures to over 300° C. over theshort period of time when a vehicle is started until it reaches cruisingspeed. The present invention uses a composite material having sufficientrigidity to withstand erosion from exhaust gases, and which alsoprovides mechanical and thermal shock resistance.

[0015] The composite material comprises inorganic fibers and/orinorganic particles. The composite may optionally include one or moreadditional binders.

[0016] Fibers useful in the practice of the invention include fibersmade from alumina-boria-silica, alumina-silica, alumina-phosphoruspentoxide, zirconia-silica, zirconia-alumina, and alumina. The fiberscan be formed by processes known in the industry such as by blowing orspinning. A useful process is spinning of a sol gel solution. Usefulfibers are commercially available under the tradenames SAFFIL from ICIChemicals & Polymers, FIBERMAX from Unifrax Co., ALCEN from Denka, andMAFTECH from Mitsubishi.

[0017] The fibers can be used as fibers or they may be used as a fibrousmat. A mat of fibers can be formed by blowing the fibrous material ontoa collection screen as is practiced in the nonwoven industry. A usefulcommercially available fiber mat is SAFFIL LD alumina fiber mat from ICIChemicals & Polymers.

[0018] The cone can also be formed from inorganic particulate materialssuch as clays, ceramic or glass powders, ceramic or glass beads, andhollow ceramic or glass spheres. Additionally, combinations of fibersand particulates can be used.

[0019] The fibers and particles can act as binders. When the fibersand/or particles are heated to elevated temperatures, e.g., over 500°C., they can melt or be softened sufficiently to bond to other fibersand particles in the cone. The fibers and particles can also besintered. By selecting fibers or particles having different meltingpoints, it is possible to get the achieve various modes of bonding themtogether. For example, a combination of glass fibers and ceramic fiberscan bond because the glass fibers soften and can melt at temperatureslower than the melting temperatures of the ceramic fibers. Additionally,the ceramic fibers can be sintered to other ceramic fibers withoutsubstantial melting of the fibers.

[0020] It may be useful to add other binders to assist in processing orto provide more strength at elevated temperatures. Organic binders canbe used to hold the inorganic materials together at room temperature toform the cone. When the cone is heated above about 300° C., the organicbinder bums off leaving the cone which can then be fired at elevatedtemperatures to sinter the inorganic materials together. Organic bindersare particularly useful for molding and injection molding processes.Useful organic binders include low melting temperatures waxes andpolyethylene glycol.

[0021] Inorganic binders can also be used. These binders include sol andsol-gel materials such as alumina sols, colloidal silica suspensions,refractory coatings such as silicon carbide suspensions, and solutionssuch as a monoaluminum phosphate solution. Colloidal silica suspensionsare commercially available from Nalco Co. under the NALCO tradename.

[0022] The inorganic binders can be incorporated into the cone by addingthe binders to the composition for forming the cone, infiltrating aformed cone with the sol or suspension, or by brushing a refractorycoating or solution onto a surface of the cone. Inorganic binders helpto stiffen the cones. When a binder solution or coating is applied onlyto one surface of the cone, e.g. the inside surface, the inside surfacebecomes more rigid while the outer surface can remain compressible. Inuse, the binders on the surface can help prevent erosion of the conefrom hot exhaust gases.

[0023] Other adjuvants may also be included to aid in processing such asdispersing aids, wetting agents, thickness, and the like.

[0024] As described below in the Examples, the free-standing fibrous endcone may be formed in a variety of manners such as with a flexible mold,slush molding, press molding, or injection molding. Mats of fibers canalso be formed in a manner similar to papier-mache in which strips ofthe fibrous mat are saturated in a binder solution and laid inoverlapping fashion on a conical surface. As detailed below, each ofthese methods of forming a free-standing fibrous end cone results in acone which is resistent to damage from exposure to hot exhaust gases,thermal shock, and road shock.

[0025] The end cone is typically secured within an outer metal end cone.The metal end cone is made of high temperature resistant metals such asstainless steel and Inconel. The end cone may be secured within theouter metal end cone 26 of a pollution control device in a variety ofmanners. For example, as seen in FIG. 2, fibrous end cone 40 iscompressed against monolith 18 and mounting mat 22 such that the fibrousend cone 40 is restrained from movement. Alternatively or in addition tosuch a frictional engagement, tabs 42 could be used to restrain fibrouscone 40 within an outer end cone 26, as illustrated in FIG. 3. Tabs 42are shown extending from exhaust pipe 44, but could also extend fromouter cone 26 or casing 12, for example. Instead of individual tabs 42as seen in FIG. 3, a solid retaining ring (not shown) could also beused. Of course, fibrous end cone 40 could be restrained within outerend cone 26 in a variety of other manners, depending upon the particularapplication desired by the user.

[0026] Objects and advantages of this invention are further illustratedby the following examples, but the particular materials and amountsthereof should not be construed to unduly limit this invention. Allparts and percentages are by weight unless stated otherwise. Althoughthe Examples pertain to an insulating end cone for use with a catalyticconverter, the present invention is equally applicable for use in otherareas of an exhaust system, such diesel particulate filters or traps,exhaust manifolds and exhaust pipes. The usefulness of the invention islikewise not limited to the conical shape of the Examples, but rather isuseful in any high temperature application where an inner insulatingliner is required and the use of a separate inner protective surface isnot desired.

TEST PROCEDURES

[0027] Hot Shake Test

[0028] The Hot Shake Test is used to evaluate an end cone for use with acatalytic converter by subjecting a catalytic converter with the endcone to vibration and hot gas from either a gasoline engine (Mode 1) orhot air (Mode 2). The two test modes are discussed more fully below.

[0029] MODE 1—A catalytic converter, with the end cone mounted securelywithin it, is attached to a solid fixture atop a shaker table (Model TC208 Electrodynamic Shaker Table from Unholtz-Dickie Corp., Wallingford,Conn.). The catalytic converter is then attached through a flexiblecoupling to the exhaust system of a Ford Motor Co. 7.5 literdisplacement V-8 gasoline powered internal combustion engine coupled toan Eaton 8121 Eddy-current dynamometer. The converter is tested using aninlet exhaust gas temperature of 900° C. at an engine speed of 2200 rpmwith a 30.4 kg-meter load, while shaking the converter at 100 Hz and 30g's acceleration on the shaker table. The converter is tested underthese conditions for 25 hours. The converter is then disassembled andthe end cone examined visually for signs of disintegration, erosion, andcracking. For a successful test, the end cone should be intact andexhibit no visible damage.

[0030] MODE 2—This test mode is conducted in a manner similar to testMode 1. A catalytic converter and end cone are mounted to a shaker table(available from Unholtz-Dickie) which shakes the converter with anacceleration of 30 g's at a frequency of 100 Hz. The heat source is anatural gas burner which supplies an inlet gas temperature of 900° C.The converter is subjected to three cycles of heating and cooling(during vibration), where a cycle includes a heating period to attain agas inlet temperature of 900° C., maintaining the inlet gas temperatureat 900° C. for an 8-hour period, and cooling to ambient temperature(about 21° C.). As in Mode 1, the end cone should not exhibit anyvisible signs of damage.

EXAMPLE 1

[0031] Example 1 illustrates how a ceramic fiber end cone was preparedusing a flexible mold and a fiber mixture having an organic binder. (Thesame composite mixture could also be injection molded).

[0032] A rubber mold was prepared by mixing 10 parts of a roomtemperature curing rubber (SILASTIC K RTV Silicone Rubber Base availablefrom Dow Corning Co.) and 1 part curing agent (SILASTIC K RTV CuringAgent available from Dow Corning Co.). The rubber mixture was moldedaround a steel cone master having the desired finished dimensions of thefiber cone. The mold was cured for 24 hours at room temperature(approximately 21° C.).

[0033] Glass fibers (6.35 mm long S-2 Glass Fibers available fromOwens-Corning Fiberglas Corp.) were heat cleaned and crushed to a fiberlength of about 0.5 mm. Ceramic fibers (SAFFIL ceramic fibers from ICIChemicals & Polymers Ltd.) were milled to a length of about 0.25 mm. Amixture of fibers was prepared by mixing 37.8 grams each of the crushedglass and ceramic fibers. The fiber mixture was then poured into aplanetary mixer (Model LDM-1 gallon Ross mixer available from CharlesRoss & Son Co.) containing 150 grams of binder (polyethylene glycol 1000m.w. available from Aldrich Chemical Inc.) and 0.75 gram of a dispersingaid (KD-5 dispersant available from ICI Americas). The mixture washeated to 100° C. in the mixer to melt the binder, and then mixed undera vacuum of 25 mm Hg for about 30 minutes. The resulting fiber-bindermixture was poured into the rubber mold which had been heated to 40° C.The filled mold was then placed in a vacuum chamber affixed to avibrating table (SYTRON vibration table from FMC Corp.) The vacuumchamber was evacuated to 30 mm Hg, and the table was vibrated for 5minutes to deaerate the mixture and to enhance the flow of the mixtureinto the mold. The mold was then removed from the vacuum chamber andcooled to room temperature. The hardened fiber cone was removed from themold, packed in a bed of hollow alumina beads (1.5 mm diameter beadsavailable from Microcel Technologies, Inc.) , and heated to 250° C. forabout 3 hours. The beads were used to prevent the cone from slumping andbecoming deformed while a substantial portion of the binder baked out.The cone was then removed from the bed and fired in a kiln at 1100° C.for 4 hours to bond the fibers in the cone. The cone was cooled to roomtemperature, inserted into a metal cone housing for a catalyticconverter, and subject to the Hot Shake Test—Mode 2 described above.After testing, the cone was found to be intact and exhibited no crackingor other visible signs of erosion or disintegration.

EXAMPLES 2-4

[0034] Examples 2-4 illustrate how a ceramic end cone was prepared usinga slurry of water and ceramic fibers. For each of Examples 2-4, aconical mold was prepared by cutting and fabricating a sheet ofperforated sheet metal to the shape of a catalytic converter end cone.The mold was then covered with a wire screen (25 mesh). The largediameter end of the cone was sealed by taping the end shut with filamenttape, and the small diameter end of the mold was attached to a 3.8 mmdiameter vacuum hose of a vacuum cleaner (Shopvac available from Sears).

[0035] For Example 2, a slurry was prepared by mixing 14 liters of tapwater, 200 grams of ceramic fibers (7000 M ceramic fibers available fromUnifrax Co., Niagara Falls, N.Y.) with an air mixer for about 10minutes. With continued mixing, 2 liters of a colloidal silicasuspension (NALCO 2327 available from Nalco Chemical Co.) were added anddispersed.

[0036] The mold was then placed in the slurry and the vacuum was turnedon for approximately 5 seconds. The mold was immediately removed afterthe vacuum was turned off, and a 6.3 mm thick layer of fibers had beendeposited on the cone. The fiber cone was removed from the. mold anddried at 100° C. for about 2 hours.

[0037] Fiber cones for Examples 3-4 were prepared as for Example 2,except that a coating was applied with a brush to the inside surface ofeach cone. The coatings of Examples 3-4 made the inner surfaces of thecones more rigid while the outer surfaces of the cones remainedcompressible. In addition to the coatings which were used in Examples3-4, it is also contemplated that other coatings such as a SiliconCarbide suspension (available from ZYP Coatings, Inc.) could also beused. The coatings for each example were as follows: Example 3 Colloidalsilica suspension (Nalco 2327) Example 4 Monoaluminum phosphate (50%Solution, Technical Grade available from Rhone-Poulenc Basic ChemicalCo.)

[0038] The cones of Examples 2, 3, and 4 were tested using the abovedescribed Hot Shake Test—Mode 2, and did not exhibit any cracking,disintegration, or erosion.

EXAMPLE 5

[0039] Example 5 illustrates how a ceramic end cone was prepared using aceramic fiber mat material. A ceramic fiber mat (SAFFIL Type LD Matavailable from ICI Chemicals and Polymers) was cut into strips measuringapproximately 5.1 cm by 10.2 cm. The strips were dipped into a colloidalsilica suspension (NALCO 2327), and applied on the inside surface of anouter metal cone portion of a catalytic converter. (The outer end coneacted as a forming mold). The strips were overlapped and layered to formcone having a thickness of about 6.35 mm. An inner cone of the catalyticconverter (acting as an interior mold for the strips) was then forcedover the layers to sandwich the layers of mat material between theexterior and interior metal end cones. The assembly was dried at 100° C.for approximately 5 hours in an air oven. The inner metal cone was thenremoved, and the outer metal cone with the layered mat was heated to900° C. for about 1 hour to form a rigid fiber cone. The fiber cone wasthen removed and subjected to the Hot Shake Test—Mode 1. The cone didnot exhibit any cracking, disintegration, or erosion.

[0040] The test results of Example 1-5 demonstrate that the freestanding fiber composite end cone can withstand the exhaust gas flowsand the vibrational shaking of an exhaust after-treatment environment.

[0041] In addition to the Examples provided herein, it is alsocontemplated that the free-standing fiber end cone may also be formed byadditional methods, such as injection molding.

[0042] Although the present invention has been described with referenceto preferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention.

What is claimed is:
 1. An article comprising a molded, self-supportinginsulating cone having dimensions suitable for use in an end cone regionof a pollution control device, said insulating cone comprising inorganicmaterials comprising inorganic fibers, inorganic particles, orcombinations thereof, wherein the inorganic materials are boundtogether.
 2. The article of claim 1, wherein the inorganic materialcomprises inorganic fibers comprising alumina-boria-silica,alumna-silica, alumina-phosphorous pentoxide, zirconia-silica,zirconia-alumina, or alumina.
 3. The article of claim 1, wherein theinorganic material comprises inorganic fibers prepared using a sol gelprocess.
 4. The article of claim 1, wherein the inorganic materialcomprises inorganic particles comprising clays, ceramic or glasspowders, ceramic or glass beads, or hollow ceramic or glass spheres. 5.The article of claim 1, wherein the insulating cone further comprisingan organic binder.
 6. The article of claim 1, wherein the insulatingcone further comprises an inorganic binder.
 7. The article of claim 6,wherein the inorganic binder comprises an alumina, colloidal silica,silicon carbide, or monoaluminum phosphate.
 8. The article of claim 6,wherein the inorganic binder is applied to one surface of the molded,self-supporting insulating cone.
 9. The article of claim 1, wherein theinorganic material comprises ceramic fibers and glass fibers.
 10. Amethod of forming a self-supporting insulating cone, said methodcomprising: preparing a mold having the shape and dimensions of an endcone for a pollution control device; forming a mixture comprisinginorganic materials and an optional binder, said inorganic materialcomprising inorganic fibers, inorganic particles, or a combinationthereof; binding together the inorganic materials in the mixture;placing the mixture in the mold; and molding the inorganic material intoa three-dimensional shaped insulation material.
 11. The method of claim10, wherein the inorganic material comprises inorganic fibers comprisingalumina-boria-silica, alumna-silica, alumina-phosphorous pentoxide,zirconia-silica, zirconia-alumina, or alumina.
 12. The method of claim10, wherein the inorganic material comprises at least one inorganicfiber prepared using a sol gel process.
 13. The method of claim 10,wherein the inorganic material comprises inorganic particles comprisingclays, ceramic or glass powders, ceramic or glass beads, or hollowceramic or glass spheres.
 14. The method of claim 10, wherein themixture further comprises an organic binder.
 15. The method of claim 10,wherein the mixture comprises ceramic fibers and further comprises anorganic binder.
 16. The method of claim 10, wherein the mixture furthercomprises an inorganic binder.
 17. The method of claim 16, wherein theinorganic binder comprises an alumina, colloidal silica, siliconcarbide, or monoaluminum phosphate.
 18. The method of claim 10, whereinthe inorganic material comprises ceramic fibers and glass fibers. 19.The method of claim 10, further comprising brushing a refractory coatingor solution onto a surface of the three-dimensional insulation material.20. A method of forming a free-standing fibrous end cone for positioningwithin a metallic end cone of a pollution control device, the methodcomprising: providing a mold having the dimensions of the inside surfaceof an outer metal end cone portion of a pollution control device;saturating strips of a ceramic fiber mat with a colloidal silicasuspension; laying the saturated ceramic fiber strips on the insidesurface of the mold; compressing the saturated ceramic fiber stripsagainst the mold to provide the desired outer and inner diameter of theinsulating end cone; and removing the fibrous insulating end cone fromthe mold.